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HG: Homegrown Column April 25, 2009

Last year, I lost my squash to squash bugs. Will marigolds planted in an area where zucchini plants are keep squash bugs off the plants?
Thank you.
— Lottie

I’m afraid planting marigolds won’t help you with squash bugs a whole lot.

Squash bugs are a terrible problem on all the cucurbits but especially on squash and pumpkins. You’ll have to use some different methods to control them.

A full-grown squash bug is difficult to control, so starting early is important in getting on top of this pest.

The smaller the insect, the easier it is to control.

The first thing to do is to monitor your plants at least once a week, looking for squash bug eggs on the underside of the leaves. They’re pretty easy to spot. They’re football-shaped and reddish brown to orange in color.

Squashing the eggs keeps the next generation from joining in the fight you already have on your hands.

This alone isn’t enough to control the problem. It just makes the job easier.

You’ll have to apply some insecticides to kill the existing insects.

If you’re looking for an organic material, try Diatomaceous Earth, Sabadilla or Neem.
Diatomaceous Earth is a naturally occurring mineral made up of fossilized plankton-like organisms called diatoms, which form a sharp, hard shell.

To us, the diatomaceous earth feels smooth, but to an insect it’s like crawling through a barrel of glass shards and barbed wire. It abrades the bug’s waxy “skin,” causing lots of tiny cuts and punctures. The result is that the insect desiccates and dies.

Just sprinkle it out at the base of the plant and on the underside of the leaves and be sure to wear a dust mask as the dust can irritate some people.

The only problem with it is that when it gets wet, it loses its effectiveness and will need to be reapplied.

Sabadilla is a botanical insecticide derived from the seeds of a South American lily. It works extremely well on squash bug, but it has become very difficult to find the past several years.

Neem is an extract from a bean from a tree native to India, where it’s been used for years and years. It’s not precisely a poison that kills the insect but rather acts either as a repellent, an “anti-feedant” (causes the insect to stop feeding), or as a growth regulator that prevents the normal growth of the insect, leading to its death.

Honestly, I’ve been less than impressed with Neem’s effectiveness.

Another non-toxic method of control is using row covers. This is a light spun-bonded fabric that’s placed over your plants to physically keep bugs away from them.

It needs to be in contact with the ground on all sides of the plant, or simply cover the entire garden with it. It’s permeable, so air and water will penetrate it, and most of the covers will transmit about 90 percent of the light so your plants will grow just fine.

Though this works well for a lot of different insect problems, I don’t think in this case that it’s a good solution.

Squash need bees and flies to pollinate the flowers and the row cover prevents them from doing that.

You can also cut down squash bug numbers by placing flat boards or shingles on the ground near your squash plants. The bugs tend to congregate there at night and the boards can be thrown away (with the bugs) early the next morning, or you could just squish them.

One last organic method is to practice what’s called good sanitation. That is, this fall when the garden is done, be sure to remove all the old debris from the garden.

The insect winters as an adult, hiding in nooks and crannies, and dead leaves and debris are favorite spots for this guy.

There are several synthetic insecticides that do a good job on squash bugs. Again, start early, because a small, immature bug is much easier to kill than a full grown adult. Also, because squash bugs tend to spend most of their time around the base of the stems of plants and on the undersides of the leaves, applying any insecticide should concentrate on those areas.

Permethrin and Bifenthrin both do a really good job. You might see some recommendations to use Sevin, but I don’t think it works all that well on them.

Since squash plants depend on bees and flies for pollination, avoid spraying when these little helpers are present. Spray only when they’re not active, primarily late in the day.